View Code of Problem 1042

//Time:1508ms
//Memory:0KB
//Length:1496B
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <queue>
#include <cstring>
using namespace std;
#define MAXN 710
#define MAXM 60010
#define MOD 1000000007
#define INF 1000000007

int he[MAXN],to[MAXM],nex[MAXM],top;
int fa[MAXN],len[MAXN],ans;
bool vi[MAXN];
void add(int u,int v)
{
    to[top]=v;
    nex[top]=he[u];
    he[u]=top++;
}
int bfs(int s)
{
    memset(vi,0,sizeof(vi));
    queue<int> que;
    vi[s]=1,len[s]=0;
    fa[s]=-1;
    que.push(s);
    while(que.size())
    {
        s=que.front();
        que.pop();
        if(len[s]*2-1>ans)   break;
        for(int i=he[s];i!=-1;i=nex[i])
            if(!vi[to[i]])
            {
                vi[to[i]]=1;
                len[to[i]]=len[s]+1;
                fa[to[i]]=s;
                que.push(to[i]);
            }
            else    if(to[i]!=fa[s])
                ans=min(ans, len[s]+len[to[i]]+1);
    }
    return INF;
}
int main()
{
    //freopen("/home/moor/Code/input","r",stdin);
    int ncase,n,m;
    scanf("%d",&ncase);
    for(int hh=1;hh<=ncase;++hh)
    {
        memset(he,-1,sizeof(he));
        top=0;
        scanf("%d%d",&n,&m);
        for(int i=0;i<m;++i)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            add(a,b);
            add(b,a);
        }
        ans=INF;
        for(int i=0;i<n&&ans>3;++i)
            bfs(i);
        printf("Case %d: ",hh);
        if(ans==INF)    printf("impossible\n");
        else    printf("%d\n",ans);
    }
    return 0;
}